This operation relates the external protocols in the numerator and denominator of the Crooks relation. In stochastic thermo, the entropy production is proportional to the log of (-5[1])the following: the probability of a trajectory, over the probability of the trajectory (15[1])under this operation. In quantum mechanics, this (15[1])operation is (15[1])an anti-unitary operator that [emphasize] commutes with the Hamiltonian. (15[1])Spin-1/2 systems that are invariant under this operation satisfy (15[1])(*) Kramers’ theorem. Magnetic fields break symmetry under this operation, which is unified with (15[1])symmetry under charge (-5[1])conjugation and parity inversion. (10[1])Loschmidt’s paradox (10[1])asks how it is possible (10[2])for Newton’s laws, which are invariant under this operation, to give rise to a quantity like entropy that only increases. For 10 (10[1])points, name this operation analogized to playing a movie backwards. ■END■